1. Field of the Invention
The invention relates generally to the field of oil and gas well services. More specifically, the present invention relates to an apparatus that provides a pressure seal around a wireline during oil field service operations.
2. Description of Related Art
Numerous techniques, generally known as well logging, exist for collecting geological data from oil and/or gas wells, where the geological data is useful for locating potential hydrocarbon bearing reservoirs. Well logging is also used for estimating the capacity of the potential hydrocarbon bearing reservoirs. Many types of well logging practices exist. They include neutron logs, induction logs, and acoustic logs. In each of the aforementioned well logging techniques a well logging tool is deposited into the wellbore and travels through the well bore collecting geological data about the region surrounding the well bore. Generally the well logging tool produces a signal, either electrical, nuclear, or acoustical, which is directed into the area adjacent the well bore. The reflection or propagation of the emitted signal is then retrieved by the tool or by another piece of equipment suitably located. The retrieved signals are stored and analyzed in order to evaluate the potential for hydrocarbon production in the particular geological formation being analyzed, monitor reservoir performance, or to evaluate wellbore mechanical integrity.
Generally, the well logging tool is inserted into the well bore attached to a wireline. The tool is raised and lowered by the wireline, and data is transmitted through the wireline for introducing signals to the well logging tool from the surface. The wire line can also transmit data recovered from within the well bore to the surface for collection and analysis.
As a secondary safety measure, a pressure containment apparatus, or pack off head, is often installed on the well during wireline operations. Wireline (or slick-line) pack off heads (oil savers) have been used by the oil field service industry for many years. A pack off head is designed to make a pressure seal around a wireline to contain the well pressure during trips in and out of the well. If during wireline operations a well kick were experienced, an unsafe condition would occur if the well head was not contained but instead left open to atmosphere. A typical pack off head includes a hard rubber insert with a passage where the wire line passes through the annulus. To seal around the wireline, the hard rubber insert is axially compressed, which reduces the cross sectional area of the passage. Reducing the cross sectional area of the passage causes the inner radius of the passage to fit snugly around the outer radius of the wire line, thus preventing fluid flow through the passage. Although the passage snugly seals around the outer radius of the wire line, the wire line is still able to freely traverse through the passage.
Traditionally, pack off heads have been manual or hydraulic. A manual style pack off head is usually comprised of a threaded cap that compresses the rubber packing element as the cap is screwed down onto the head assembly. This operation is typically performed by hand. The hydraulic style pack off head has a hydraulic cylinder that is expanded via hydraulic pressure provided by a hand pump connected to the head by a hydraulic hose. The pack off head cylinder expands as pressure is supplied to it, expansion of the pack off head cylinder in turn compresses the pack off element. Both the manual and the hydraulic pack off heads compress a packing element to provide a seal around the wireline and both require personnel to perform this function.
Therefore, a method or an apparatus is desired that provides an automatic pressure sealing function around a wireline when the pack off head is located in an area that is not accessible to be either manually or hydraulically operated while a wireline is being lowered into and drawn from a hydrocarbon producing wellbore.